The present invention relates generally to data storage systems. More particularly, the present invention relates to the selection of read channel parameter values to optimize the operational performance of a disc drive data storage system.
A typical disc drive includes one or more discs mounted for rotation on a hub or spindle. A typical disc drive also includes a transducer supported by a hydrodynamic air bearing which flies above each disc. The transducer and the hydrodynamic air bearing are collectively referred to as a data head. A drive controller is conventionally used for controlling the disc drive based on commands received from a host system. The drive controller controls the disc drive to retrieve information from the discs and to store information on the discs.
An electromechanical actuator operates within a negative feedback, closed-loop servo system. The actuator moves the data head radially over the disc surface for track seek operations and holds the transducer directly over a track on the disc surface for track following operations.
In a disc drive employing magnetic discs, for example, information is typically stored in concentric tracks on disc surfaces by providing a write signal to the data head to encode flux reversals on the disc surface. The flux reversals represent the data to be stored. In retrieving data from the disc, the drive controller controls the electromechanical actuator so that the data head flies above the magnetic disc, sensing the flux reversals on the magnetic disc, and generating a read signal based on those flux reversals. The read signal is typically conditioned and then decoded by the drive controller to recover data represented by flux reversals stored in the magnetic disc, and consequently represented in the read signal provided by the data head.
A typical readback system includes the data head, a preamplifier, a read channel including filtering circuitry and data detection circuitry, and error detection and correction circuitry. The readback system can be implemented either as discrete circuitry, or in a drive controller associated with the disc drive.
In disc drives, it is important that the error rate per number of bits recovered (the bit error rate) be maintained at a relatively low level. Thus, during disc drive development and manufacture, tests are conducted to determine the accuracy of data interpretation by the read channel of the readback system. Current techniques for obtaining optimum read channel parameter values typically involve selecting a set of initial parameter values, writing test data on one or more tracks, reading the data and calculating the bit error rate for the initial set of values. The process is then repeated with individual parameters of the initial set of parameter values sequentially incremented so that a population of error rates is obtained for a range of parameter values. Optimum parameter values are then selected from the range of parameter values. These techniques are complex and involve numerous calculations. Further, the bit error rate only represents the total effect of equalization of the read channel and the response of individual component circuits of the read channel are not examined during the process of selection of optimum parameter values.
The present invention provides a solution to these and other problems and offers other advantages over the prior art.
Various embodiments of the present invention relate to obtaining optimum parameter values for a read channel employed in a disc drive storage system by spectral analysis of outputs of component circuits of the read channel, thereby addressing the above-mentioned problems.
A method and apparatus for obtaining optimum parameter values for a read channel employed in a disc drive storage system are provided in which data having a known pattern is written on a disc surface of the disc drive storage system. The data written on the disc surface is then read to obtain a readback signal. The readback signal is passed through the read channel. A readback signal response is obtained at an output test point of the read channel. The readback signal response at the output test point is compared with a target response of the read channel at the output test point. The comparison is carried out using frequency spectral analysis. At least one parameter of the read channel is adjusted if the readback signal response substantially differs from the target response.
These and various other features as well as advantages which characterize various embodiments of the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.